Mims: Tower cranes give lift to construction

Updated 6:01 pm, Friday, October 19, 2012

Three giant tower cranes are being used in the construction of Bexar County's University Hospital expansion.

Three giant tower cranes are being used in the construction of Bexar County's University Hospital expansion.

Photo: Forrest M. Mims III, For The Express-News

Mims: Tower cranes give lift to construction

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At night, the skyline of northwest San Antonio is punctuated by three tall towers illuminated by bright lights. Each tower has a lengthy cross member, which is also illuminated.

Recently I observed those giant towers from directly under one of them. They are giant tower cranes whose operators must climb a dozen or more steel ladder sections to reach their perch. From there they deftly maneuver heavy loads of construction equipment and materials over and around the $900 million expansion of Bexar County's University Hospital.

The construction of today's high-rise buildings is dependent on various kinds of tower cranes, a technology that springs from hundreds of years of construction science and engineering. The building materials range from brick and concrete, first developed many centuries ago, to the very latest products from materials science.

You can watch the tower cranes at the University Hospital expansion project from one of the restaurants across from the hospital on Medical Drive. Look closely and you will see workers scattered throughout the site attaching or removing loads from the cranes, installing pipes and bolting steel beams to concrete floors.

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While the three tower cranes receive most attention, smaller cranes are also employed at the project. I watched a crew use a truck-mounted crane to lift a steel beam several stories high. A team of three men pulled the beam onto a row of bolts emerging from the side of a concrete floor. The men then leaned over the space below to secure the beam in place with nuts and wrenches.

While this work was under way, a tower crane team high above was preparing to lift a large structure from the corner of the uppermost story of the new building. After the team checked and rechecked the support cables, the operator was given the signal to raise the heavy load and quickly move it a hundred feet or so to where a second crew was waiting.

Meanwhile, ground workers were connecting still another big load to the cable of a tower crane whose base is bolted to a concrete foundation adjacent to the walkway where I stood.

The operator raised the load a foot or so while two men carefully inspected the straps that secured it to the crane's cable. Then one man spoke into a radio or phone, and the heavy load was suddenly and smoothly hoisted up into the sky.

Tower cranes have revolutionized building construction. During a visit to Hong Kong in 1967, I saw several tall buildings being constructed inside intricate frameworks of bamboo scaffolding. The Chinese have long since switched to tower cranes.